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with SMTP id 5614622812f47-53ccb4ea805mr3155325b6e.20.1792295492629; Sat, 17 Oct 2026 20:51:32 -0700 (PDT) Date: Sat, 17 Oct 2026 20:51:32 -0700 In-Reply-To: <6ad2e6e0.6814cce4.34c49f.0026.GAE@google.com> X-Google-Appengine-App-Id: s~syzkaller X-Google-Appengine-App-Id-Alias: syzkaller Message-ID: <6ad44244.7f4e89eb.3d59aa.00ac.GAE@google.com> Subject: Re: [syzbot] [x25?] possible deadlock in lapb_connect_request From: syzbot To: andrew@lunn.ch, davem@davemloft.net, edumazet@kernel.org, kuba@kernel.org, linux-kernel@vger.kernel.org, linux-x25@vger.kernel.org, ms@dev.tdt.de, netdev@vger.kernel.org, pabeni@redhat.com, syzkaller-bugs@googlegroups.com Content-Type: text/plain; charset="UTF-8" syzbot has found a reproducer for the following issue on: HEAD commit: 58161ead29e5 Merge tag 'drm-fixes-2026-10-17' of https://g.. git tree: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git console output: https://syzkaller.appspot.com/x/log.txt?x=1212098e580000 kernel config: https://syzkaller.appspot.com/x/.config?x=129d675874dbf896 dashboard link: https://syzkaller.appspot.com/bug?extid=8328573e4d0514392471 compiler: gcc (Debian 14.2.0-19) 14.2.0, GNU ld (GNU Binutils for Debian) 2.44 C reproducer: https://syzkaller.appspot.com/x/repro.c?x=1612098e580000 IMPORTANT: if you fix the issue, please add the following tag to the commit: Reported-by: syzbot+8328573e4d0514392471@syzkaller.appspotmail.com ====================================================== WARNING: possible circular locking dependency detected syzkaller #0 Not tainted ------------------------------------------------------ syz-executor333/5939 is trying to acquire lock: ffffffff91f49b18 (lapb_list_lock){++..}-{3:3}, at: lapb_devtostruct net/lapb/lapb_iface.c:102 [inline] ffffffff91f49b18 (lapb_list_lock){++..}-{3:3}, at: lapb_connect_request+0x26/0x1a0 net/lapb/lapb_iface.c:287 but task is already holding lock: ffff88807a54cf00 (&lapbeth->up_lock){+...}-{3:3}, at: spin_lock_bh include/linux/spinlock.h:353 [inline] ffff88807a54cf00 (&lapbeth->up_lock){+...}-{3:3}, at: lapbeth_xmit+0x24/0x250 drivers/net/wan/lapbether.c:191 which lock already depends on the new lock. the existing dependency chain (in reverse order) is: -> #3 (&lapbeth->up_lock){+...}-{3:3}: lock_acquire kernel/locking/lockdep.c:5942 [inline] lock_acquire+0x1d1/0x380 kernel/locking/lockdep.c:5899 __raw_spin_lock_bh include/linux/spinlock_api_smp.h:182 [inline] _raw_spin_lock_bh+0x33/0x40 kernel/locking/spinlock.c:205 spin_lock_bh include/linux/spinlock.h:353 [inline] lapbeth_xmit+0x24/0x250 drivers/net/wan/lapbether.c:191 __netdev_start_xmit include/linux/netdevice.h:5432 [inline] netdev_start_xmit include/linux/netdevice.h:5441 [inline] xmit_one net/core/dev.c:3953 [inline] dev_hard_start_xmit+0x121/0x760 net/core/dev.c:3969 __dev_queue_xmit+0x1c25/0x4a40 net/core/dev.c:4958 dev_queue_xmit include/linux/netdevice.h:3464 [inline] tx+0xc4/0x130 drivers/block/aoe/aoenet.c:62 kthread+0x1d8/0x3c0 drivers/block/aoe/aoecmd.c:1241 kthread+0x373/0x450 kernel/kthread.c:436 ret_from_fork+0x730/0xd60 arch/x86/kernel/process.c:158 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245 -> #2 (_xmit_X25#2){+...}-{3:3}: lock_acquire kernel/locking/lockdep.c:5942 [inline] lock_acquire+0x1d1/0x380 kernel/locking/lockdep.c:5899 __raw_spin_lock include/linux/spinlock_api_smp.h:190 [inline] _raw_spin_lock+0x2e/0x40 kernel/locking/spinlock.c:173 spin_lock include/linux/spinlock.h:347 [inline] __netif_tx_lock include/linux/netdevice.h:4841 [inline] __dev_queue_xmit+0x1ac6/0x4a40 net/core/dev.c:4952 neigh_output include/net/neighbour.h:560 [inline] ip_finish_output2+0x851/0x2400 net/ipv4/ip_output.c:236 __ip_finish_output.part.0+0x444/0x6f0 net/ipv4/ip_output.c:314 __ip_finish_output net/ipv4/ip_output.c:302 [inline] ip_finish_output net/ipv4/ip_output.c:324 [inline] NF_HOOK_COND include/linux/netfilter.h:314 [inline] ip_output+0x39b/0xc10 net/ipv4/ip_output.c:437 dst_output include/net/dst.h:471 [inline] ip_local_out+0x193/0x1f0 net/ipv4/ip_output.c:131 iptunnel_xmit+0x722/0xd30 net/ipv4/ip_tunnel_core.c:97 ip_tunnel_xmit+0x1b91/0x3210 net/ipv4/ip_tunnel.c:848 __gre_xmit+0x91a/0xc90 net/ipv4/ip_gre.c:488 gre_tap_xmit+0x44e/0x700 net/ipv4/ip_gre.c:783 __netdev_start_xmit include/linux/netdevice.h:5432 [inline] netdev_start_xmit include/linux/netdevice.h:5441 [inline] xmit_one net/core/dev.c:3953 [inline] dev_hard_start_xmit+0x121/0x760 net/core/dev.c:3969 sch_direct_xmit+0x1b2/0xc70 net/sched/sch_generic.c:372 __dev_xmit_skb net/core/dev.c:4277 [inline] __dev_queue_xmit+0x2812/0x4a40 net/core/dev.c:4916 lapb_data_transmit+0x96/0xc0 net/lapb/lapb_iface.c:447 lapb_transmit_buffer+0xce/0x3a0 net/lapb/lapb_out.c:149 lapb_send_control+0x1ce/0x330 net/lapb/lapb_subr.c:251 lapb_establish_data_link+0xeb/0x110 net/lapb/lapb_out.c:163 lapb_device_event+0x315/0x580 net/lapb/lapb_iface.c:512 notifier_call_chain+0x99/0x3f0 kernel/notifier.c:85 call_netdevice_notifiers_info+0xbe/0x110 net/core/dev.c:2275 call_netdevice_notifiers_extack net/core/dev.c:2313 [inline] call_netdevice_notifiers net/core/dev.c:2327 [inline] __dev_notify_flags+0x22c/0x4b0 net/core/dev.c:9896 netif_change_flags+0x108/0x160 net/core/dev.c:9925 dev_change_flags+0xba/0x260 net/core/dev_api.c:68 devinet_ioctl+0x110b/0x1f10 net/ipv4/devinet.c:1199 inet_ioctl+0x3aa/0x3f0 net/ipv4/af_inet.c:1009 sock_do_ioctl+0x118/0x280 net/socket.c:1325 sock_ioctl+0x599/0x6b0 net/socket.c:1446 vfs_ioctl fs/ioctl.c:51 [inline] __do_sys_ioctl fs/ioctl.c:597 [inline] __se_sys_ioctl fs/ioctl.c:583 [inline] __x64_sys_ioctl+0x18e/0x210 fs/ioctl.c:583 do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline] do_syscall_64+0x123/0x790 arch/x86/entry/syscall_64.c:84 entry_SYSCALL_64_after_hwframe+0x77/0x7f -> #1 (&lapb->lock){+.-.}-{3:3}: lock_acquire kernel/locking/lockdep.c:5942 [inline] lock_acquire+0x1d1/0x380 kernel/locking/lockdep.c:5899 __raw_spin_lock_bh include/linux/spinlock_api_smp.h:182 [inline] _raw_spin_lock_bh+0x33/0x40 kernel/locking/spinlock.c:205 spin_lock_bh include/linux/spinlock.h:353 [inline] lapb_unregister+0x112/0x400 net/lapb/lapb_iface.c:187 lapbeth_close+0x56/0x90 drivers/net/wan/lapbether.c:350 __dev_close_many+0x312/0x710 net/core/dev.c:1798 __dev_close net/core/dev.c:1811 [inline] __dev_change_flags+0x307/0x850 net/core/dev.c:9853 netif_change_flags+0x8d/0x160 net/core/dev.c:9920 dev_change_flags+0xba/0x260 net/core/dev_api.c:68 devinet_ioctl+0x110b/0x1f10 net/ipv4/devinet.c:1199 inet_ioctl+0x3aa/0x3f0 net/ipv4/af_inet.c:1009 sock_do_ioctl+0x118/0x280 net/socket.c:1325 sock_ioctl+0x599/0x6b0 net/socket.c:1446 vfs_ioctl fs/ioctl.c:51 [inline] __do_sys_ioctl fs/ioctl.c:597 [inline] __se_sys_ioctl fs/ioctl.c:583 [inline] __x64_sys_ioctl+0x18e/0x210 fs/ioctl.c:583 do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline] do_syscall_64+0x123/0x790 arch/x86/entry/syscall_64.c:84 entry_SYSCALL_64_after_hwframe+0x77/0x7f -> #0 (lapb_list_lock){++..}-{3:3}: check_prev_add+0xeb/0xe60 kernel/locking/lockdep.c:3209 check_prevs_add kernel/locking/lockdep.c:3328 [inline] validate_chain kernel/locking/lockdep.c:3952 [inline] __lock_acquire+0x1528/0x1f40 kernel/locking/lockdep.c:5288 lock_acquire kernel/locking/lockdep.c:5942 [inline] lock_acquire+0x1d1/0x380 kernel/locking/lockdep.c:5899 __raw_read_lock_bh include/linux/rwlock_api_smp.h:192 [inline] _raw_read_lock_bh+0x3f/0x70 kernel/locking/spinlock.c:287 lapb_devtostruct net/lapb/lapb_iface.c:102 [inline] lapb_connect_request+0x26/0x1a0 net/lapb/lapb_iface.c:287 lapbeth_xmit+0x1cb/0x250 drivers/net/wan/lapbether.c:205 __netdev_start_xmit include/linux/netdevice.h:5432 [inline] netdev_start_xmit include/linux/netdevice.h:5441 [inline] xmit_one net/core/dev.c:3953 [inline] dev_hard_start_xmit+0x121/0x760 net/core/dev.c:3969 __dev_queue_xmit+0x1c25/0x4a40 net/core/dev.c:4958 dev_queue_xmit include/linux/netdevice.h:3464 [inline] packet_xmit+0x243/0x310 net/packet/af_packet.c:277 packet_snd net/packet/af_packet.c:3149 [inline] packet_sendmsg+0x32ee/0x5040 net/packet/af_packet.c:3181 sock_sendmsg_nosec net/socket.c:800 [inline] __sock_sendmsg net/socket.c:815 [inline] __sys_sendto+0x48b/0x4e0 net/socket.c:2281 __do_sys_sendto net/socket.c:2288 [inline] __se_sys_sendto net/socket.c:2284 [inline] __x64_sys_sendto+0xe0/0x1c0 net/socket.c:2284 do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline] do_syscall_64+0x123/0x790 arch/x86/entry/syscall_64.c:84 entry_SYSCALL_64_after_hwframe+0x77/0x7f other info that might help us debug this: Chain exists of: lapb_list_lock --> _xmit_X25#2 --> &lapbeth->up_lock Possible unsafe locking scenario: CPU0 CPU1 ---- ---- lock(&lapbeth->up_lock); lock(_xmit_X25#2); lock(&lapbeth->up_lock); rlock(lapb_list_lock); *** DEADLOCK *** locks held by syz-executor333/5939: 3, last CPU#0: #0: ffffffff8fdec580 (rcu_read_lock_bh){....}-{1:3}, at: local_bh_disable include/linux/bottom_half.h:20 [inline] #0: ffffffff8fdec580 (rcu_read_lock_bh){....}-{1:3}, at: rcu_read_lock_bh include/linux/rcupdate.h:902 [inline] #0: ffffffff8fdec580 (rcu_read_lock_bh){....}-{1:3}, at: __dev_queue_xmit+0x296/0x4a40 net/core/dev.c:4872 #1: ffff888023beb558 (_xmit_X25#2){+...}-{3:3}, at: spin_lock include/linux/spinlock.h:347 [inline] #1: ffff888023beb558 (_xmit_X25#2){+...}-{3:3}, at: __netif_tx_lock include/linux/netdevice.h:4841 [inline] #1: ffff888023beb558 (_xmit_X25#2){+...}-{3:3}, at: __dev_queue_xmit+0x1ac6/0x4a40 net/core/dev.c:4952 #2: ffff88807a54cf00 (&lapbeth->up_lock){+...}-{3:3}, at: spin_lock_bh include/linux/spinlock.h:353 [inline] #2: ffff88807a54cf00 (&lapbeth->up_lock){+...}-{3:3}, at: lapbeth_xmit+0x24/0x250 drivers/net/wan/lapbether.c:191 stack backtrace: CPU: 0 UID: 0 PID: 5939 Comm: syz-executor333 Not tainted syzkaller #0 PREEMPT(full) Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 08/05/2026 Call Trace: __dump_stack lib/dump_stack.c:94 [inline] dump_stack_lvl+0x100/0x190 lib/dump_stack.c:120 print_circular_bug.cold+0x178/0x1be kernel/locking/lockdep.c:2087 check_noncircular+0x146/0x160 kernel/locking/lockdep.c:2219 check_prev_add+0xeb/0xe60 kernel/locking/lockdep.c:3209 check_prevs_add kernel/locking/lockdep.c:3328 [inline] validate_chain kernel/locking/lockdep.c:3952 [inline] __lock_acquire+0x1528/0x1f40 kernel/locking/lockdep.c:5288 lock_acquire kernel/locking/lockdep.c:5942 [inline] lock_acquire+0x1d1/0x380 kernel/locking/lockdep.c:5899 __raw_read_lock_bh include/linux/rwlock_api_smp.h:192 [inline] _raw_read_lock_bh+0x3f/0x70 kernel/locking/spinlock.c:287 lapb_devtostruct net/lapb/lapb_iface.c:102 [inline] lapb_connect_request+0x26/0x1a0 net/lapb/lapb_iface.c:287 lapbeth_xmit+0x1cb/0x250 drivers/net/wan/lapbether.c:205 __netdev_start_xmit include/linux/netdevice.h:5432 [inline] netdev_start_xmit include/linux/netdevice.h:5441 [inline] xmit_one net/core/dev.c:3953 [inline] dev_hard_start_xmit+0x121/0x760 net/core/dev.c:3969 __dev_queue_xmit+0x1c25/0x4a40 net/core/dev.c:4958 dev_queue_xmit include/linux/netdevice.h:3464 [inline] packet_xmit+0x243/0x310 net/packet/af_packet.c:277 packet_snd net/packet/af_packet.c:3149 [inline] packet_sendmsg+0x32ee/0x5040 net/packet/af_packet.c:3181 sock_sendmsg_nosec net/socket.c:800 [inline] __sock_sendmsg net/socket.c:815 [inline] __sys_sendto+0x48b/0x4e0 net/socket.c:2281 __do_sys_sendto net/socket.c:2288 [inline] __se_sys_sendto net/socket.c:2284 [inline] __x64_sys_sendto+0xe0/0x1c0 net/socket.c:2284 do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline] do_syscall_64+0x123/0x790 arch/x86/entry/syscall_64.c:84 entry_SYSCALL_64_after_hwframe+0x77/0x7f RIP: 0033:0x7ff79ae040b7 Code: 48 89 fa 4c 89 df e8 98 1d 00 00 8b 93 08 03 00 00 59 5e 48 83 f8 fc 74 1a 5b c3 0f 1f 84 00 00 00 00 00 48 8b 44 24 10 0f 05 <5b> c3 0f 1f 80 00 00 00 00 83 e2 39 83 fa 08 75 de e8 23 ff ff ff RSP: 002b:00007ffe8b1e5860 EFLAGS: 00000202 ORIG_RAX: 000000000000002c RAX: ffffffffffffffda RBX: 0000555590b13400 RCX: 00007ff79ae040b7 RDX: 0000000000000001 RSI: 00007ffe8b1e58bf RDI: 0000000000000005 RBP: 0000000000000004 R08: 00007ffe8b1e58c0 R09: 0000000000000014 R10: 0000000000000000 R11: 0000000000000202 R12: 0000000000000003 R13: 0000000000000005 R14: 00007ff79ae3d059 R15: 00007ff79ae3d044 --- If you want syzbot to run the reproducer, reply with: #syz test: git://repo/address.git branch-or-commit-hash If you attach or paste a git patch, syzbot will apply it before testing.